Blurr

I pulled into the garage last night, turned the engine off then heard some odd noises coming from under the hood and noticed that air was bubbling out of the hose that is in the radiator reservoir tank. no coolant leaks anywhere (that I can see), engine oil is clean. i opened the radiator cap this morning and it was clear as well. drove 12mi to work this morning and there was no bubbling, no leaks anywhere.

i did the HG job about 4k miles ago and this is the first time this has happened. as far as i know the coolant level has been fine all along, is it possible this is just an air-bubble that is burping out or am i looking at something much much worse?

TNRabbit

When cool, was the radiator topped off?

Blurr

not to the brim but it was definitely full.

GSGALLANT

Well, if there's anything coming out of the tube in the overflow bottle (air or coolant), it is either due to a bad rad cap (opening at too low a pressure), or because your cooling system pressure was too high. If your rad cap is fine, then the ways your cooling system can overpressize is by getting too hot, or if cylinder pressure is leaking by your head gasket into the cooling system.

If your head gaskets check out fine (leak down test), then I'd look at faulty/sticky/partially plugged thermistat, or water pump starting to wear.

As far as it being air coming out of the tube, (if your head gasket is fine) that could be the bit of air that was left in your system when you last topped it up (almost to the top)... however, in order for the air to come out through that hose, you're back at the top of my post with it being forced out by the system pressure being too high, or your rad cap being faulty.

Good luck.

Blurr

I replaced the water pump and thermostat when i did the HG job with OEM parts but i guess it is possible that they could go bad.

seems to me the only two ways air could be coming out of the overflow tube is if an air pocket was exposed and has burped its way up or air is somehow entering the cooling system from another location (head gasket or a leaky hose/fitting that i haven't found yet).

i'll keep a close eye on the coolant level, monitor the coolant and oil for any mixture of the two, and look more closely for leaks. thanks for your thoughts

mt_goat

One other possiblity is the coolant is boiling after shutdown. After shut down the head will superheat the coolant against it and if the head temp exceeds the boiling pt of your coolant you get steam bubbles in the system. Possible causes of this could be a bad radiator cap (lower pressure boils easier) or too little antifreeze to water ratio. Or you could just be running too hot.